1. Field of the Invention
The present invention relates to a band-pass filter using a diffraction grating formed in an optical waveguide, and a method of making the same.
2. Related Background Art
Optical fiber-gratings have been known as a device used in optical fiber communication systems. In an optical fiber-grating, a light component having a specific wavelength is reflected according to a period between adjacent gratings, and light components having specific wavelengths are reflected according to respective periodes between other gratings. Accordingly, since light in a specific wavelength region can be effectively reflected, the optical fiber-grating has been used as a reflecting device.
On the other hand, it has been known to combine optical fiber-gratings having different periods together so as to form a band-pass filter. An example of such a band-pass filter is disclosed in a paper titled "Fiber-grating transmission filters for use in an all-fiber demultiplexer" (OFC'94 Technical Digest: TuL6). It discloses a technique in which two pieces of optical fiber-gratings made of chirp gratings having different reflection wavelength regions are combined together, thereby transmitting therethrough light in a desired band of a specific wavelength region.